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Various forms of cobalt catalysts have been studied extensively for selective aerobic oxidation of hydrocarbons. However, it remains unclear whether cobalt can directly activate molecular oxygen under mild reaction conditions. Here we investigated the catalytic roles of cobalt in ethylbenzene oxidation with and without a hydroperoxide initiator. The contribution of different cobalt species was studied by varying the metal loading on Co-impregnated ZSM-5 samples. Quantitative EPR was used to determine the impact of cobalt catalysts on the free radical concentrations. This work provided strong evidence that cobalt, in several different forms, catalyzes hydrocarbon oxidation by facilitating peroxy bond cleavage, instead of direct oxygen activation.

Vapor phase catalytic hydrogen peroxide production by oxidation of water is possible by coupling the reaction with oxidation of an organic sacrificial reductant. It is potentially a safer process than direct synthesis from H2 and O2. Based on mechanistic information available mostly for liquid phase catalytic processes, feasible reaction mechanisms for such coupled reactions are proposed based on which desirable catalyst properties are identified. It is found that the surface-adsorbed oxygen bond is an important parameter for identifying desirable catalysts. Thermodynamics can be used to identify the types of organic oxidation reactions that can couple with water oxidation such that H2O2 formation becomes thermodynamically favorable. Reactions such as epoxidation of alkenes and selective oxidation of alkanes to alcohols cannot provide sufficient thermodynamic driving force, whereas oxidation of alcohols to aldehydes and to acids can. Finally, further research is suggested to identify catalytic properties important for H2O2 decomposition and for coupling selective oxidation of organic compounds to oxidation of H2O in order to facilitate development of H2O2 production coupled with selective organic oxidation.

Catalytic oxidation of organic pollutants is an attractive and sustainable method of water purification. This paper focuses on discussion of catalytic activity, selectivity, and stability in cataly...

Aerobic oxidation of α-C H bond of organic compounds to valuable chemicals is widely investigated in both fundamental research and industry. Due to the good stability of molecular oxygen, severe reaction conditions are generally required. Herein, by in situ synthesis we used molecular oxygen to induce cobalt nanoclusters with the sensitive catalysis in mild selective oxidation. The cobalt containing clusters with an average diameter around 0.9 nm are in situ prepared in the presence of cis-cyclooctene epoxidation and cyclooctene dimer oxide is formed at the interface to stabilize Co clusters with electron donation as an oil-soluble surfactant. The soluble clusters exhibit high activity in selective oxidation of α-C H bond of ethylbenzene into acetophenone and turnover number (TON) reaches about 7 × 104 during 50 h’ reaction at 373 K, which is around 960 times more active than the one using CoCl2 salt as the catalyst, resulting from efficient mass transportation, π bond interaction and oxygen gas activation. Extended work based on this understanding demonstrates that cobalt nanoclusters also effectively catalyze aerobic oxidation of cyclohexene.

The catalytic properties of physical mixtures of Ni particles (100–200 nm) with nanoparticles of anatase TiO2 (TiO2-A), ZrO2, Al2O3, rutile TiO2 (TiO2-R), and CeO2 were investigated for the hydrode...

Interfacial perimeter sites between metal and support are often important for catalysis. A mononuclear titanium siloxy complex III, Ti(acac)2[OSiC6H5N(OCH3)2]2 was synthesized to generate TiOx units of different degrees of clustering to decorate Au nanoparticles. Two different methods of preparation were examined; one was to deposit III onto Au/SiO2 and the other was to form III-covered Au nanoparticle first before deposition onto SiO2. The former method generated more highly dispersed TiOx units, while larger domains of TiO2 were formed with the latter method, as deduced by UV–vis and XAS characterization. A model was proposed to explain how TiOx dispersity could be related to the preparative procedures. These samples were further tested as catalysts in selective oxidation of propane in a stream of O2 and H2. They exhibited different product selectivities. The sample with more dispersed TiOx units were more selective for acetone formation versus propene formation. The results confirmed the important role of both the Au–TiOx interface at the perimeter and the extent of Ti isolation in the TiOx phase in the reaction.

Ternary metal fluoride Fe x Mn 1−x F 2 (x = 0.00, 0.25, 0.50, 0.75, and 1.00), which is a potential cathode material for next-generation Li-ion batteries, were synthesized via a convenient, low-temperature, bottom-up solution-phase method. The lattice dimensions deduced from X-ray diffraction suggested formation of homogeneous solid solutions. With increasing Fe content, the morphology of the solid changed from cubic particles to dendritic, with an average particle size of 20–40 nm. The results suggested that this synthetic method constitutes a translatable route to large-scale production of ternary metal fluoride nanoparticles.

Inverse gas chromatography (IGC) was employed in evaluating the catalytic surface of meso-microporous KIT-6 impregnated Ni (0.5–2.0 wt%) in methane dry reforming reaction. The free energy of adsorption did not changed significantly for the sample modified with highly dispersed Ni species (0.5 wt%). At higher Ni loadings, higher free energy of adsorption and enthalpy of adsorption of the probes were observed, together with high dispersive interaction and specific interaction of aromatics. The results indicated that during the impregnation, Ni species preferably penetrated into the microporous region to form Ni particles and became ‘unaccessible’. This feature was used to understand the dependence of activity on Ni loading for the gas phase catalytic methane reforming with carbon dioxide on Ni/KIT-6. The lower TOF at low metal loadings was attributed to Ni particles located in the micropores which result in diffusional constraint of reactants and products.

Electrically conducting, 3D elastomeric composite foams are fabricated successfully using multiple cycles of infusing polyurethane foams with graphene oxide sheets followed by reduction, to form coatings of reduced graphene oxide up to ∼1260 nm thick. The reduced graphene oxide coating increases the compression modulus of the composite and lowers the electrical resistance significantly compared with polyurethane foam, the extents of which increase with increasing coating thickness. The electrical resistance of the coated foams varies by as much as three orders of magnitude for coating thickness between ∼150 and ∼1200 nm, whereas the capacitance varies by one order of magnitude. Both the stress-strain and the resistance-strain behavior are highly repeatable with compression cycles performed up to 70% strain. Both SEM and X-ray tomography characterization show that deformation is mostly through bending of the pore walls up to about 20% strain, collapse of pore openings to about 60% strain, and densification beyond that. Micro-fractures also develop on the coating during the first few cycles of compression, but no obvious structural changes can be detected afterwards.

Cu-modified Au/TiO2 (anatase, 200 m2/g) has been prepared by the incipient-wetness technique with introduction of the modifier either before or after Au loading. Such catalysts gave higher catalytic activities for the water–gas shift (WGS) reaction when compared to the unmodified catalysts mainly because of the existence of a synergetic interaction between Cu and Au, as the activities of both Cu/TiO2 and Au/TiO2 are lower than that of the bimetallic system. The WGS activities of both the as-prepared Au/TiO2 and a Au–Cuc/TiO2 catalyst were found to be high and stable. The presence of nitrates on Cuc–Au/TiO2 was found to be detrimental to the activity of Au on TiO2, as a result of the poisoning of Au and enhanced Au agglomeration by NO2 formed during reaction. The activities of Au/TiO2 catalysts modified with Cu-containing acetate counterions were found to decrease during the first 30 min on stream, reaching a constant value of (45 ± 2)%. However, when the poisoning by the acetate anion was eliminated throu...

In a noncontact catalytic system, intermediaries derived from Au-catalyzed cyclooctene epoxidation effects ethylbenzene oxidation., Traditionally, a catalyst functions by direct interaction with reactants. In a new noncontact catalytic system (NCCS), an intermediate produced by one catalytic reaction serves as an intermediary to enable an independent reaction to proceed. An example is the selective oxidation of ethylbenzene, which could not occur in the presence of either solubilized Au nanoclusters or cyclooctene, but proceeded readily when both were present simultaneously. The Au-initiated selective epoxidation of cyclooctene generated cyclooctenyl peroxy and oxy radicals that served as intermediaries to initiate the ethylbenzene oxidation. This combined system effectively extended the catalytic effect of Au. The reaction mechanism was supported by reaction kinetics and spin trap experiments. NCCS enables parallel reactions to proceed without the constraints of stoichiometric relationships, offering new degrees of freedom in industrial hydrocarbon co-oxidation processes.

Grafting of pairs of functional groups onto a silica surface was demonstrated by tethering both terminals of an organochlorosilane precursor molecule, Cl2(CH3)Si(CH2)4(CO)(OSi(i-Pr)2)(CH2)2Si(CH3)Cl2, that possess a cleavable silyl ester bond, onto a silica surface. Hydrolytic cleavage of the silyl ester bond of the grafted molecule resulted in the generation of organized pairs of carboxylic acid and organosilanol groups. This organosilanol moiety was easily transformed into other functional groups through condensation reactions to form, together with the neighboring acid group, pairs such as carboxylic acid/secondary amine, carboxylic acid/pyridine, and carboxylic acid/phosphine. In the case of carboxylic acid/amine pairing, there was evidence of the formation of amide. A sample grafted with amine–carboxylic acid pairs was three times more active (per free amine) than a sample without such pairs for the nitroaldol condensation of 4-nitrobenzaldehyde and nitromethane.

The efficiency of H2O2 formation during Au/C-catalyzed aerobic oxidation of 1,2-propanediol (diol) at 35 °C increased with increasing concentrations of diol and NaOH. Diol conversion and H2O2 accumulation data collected at different concentrations of diol and NaOH could be fitted to a Langmuir–Hinshelwood kinetics model using the diolate as the reactant, indicating that the primary role of hydroxide ions is to deprotonate the diol and not as a reactant in the rate limiting step. Using the model to extrapolate the data to full surface coverage of diolate, it was found that one molecule of diol oxidized would produce one molecule of H2O2 and one molecule of lactate. At lower diolate coverages, unoccupied active sites adjacent to adsorbed hydroperoxy/peroxy enabled O O bond cleavage and lowered the H2O2 production efficiency. Catalytic degradation of H2O2 decreased its production efficiency, and accumulation of trace amounts of heavy products likely caused the slow catalyst deactivation.

There is an urgent need to provide adequate and sustainable supplies of water and food to satisfy the demand of an increasing population. Catalysis plays important roles in meeting these needs by facilitating the synthesis of hydrogen peroxide that is used in water decontamination and chemicals production, and ammonia that is used as fertilizer. However, these chemicals are currently produced with processes that are either very energy-intensive or environmentally unfriendly. This article offers the perspectives of the challenges and opportunities in the production of these chemicals, focusing on the roles of catalysis in more sustainable, alternative production methods that minimize energy consumption and environmental impact. While not intended to be a comprehensive review, the article provides a critical review of selected literature relevant to its objectives, discusses areas needed for further research, and potential new directions inspired by new developments in related fields. For each chemical, production by thermal, electro-, and photo-excited processes are discussed. Problems that are common to these approaches and their differences are identified and possible solutions suggested.

Amine-functionalized siloxane oligomers were synthesized and used successfully to prepare colloidal Au particles smaller than 1 nm. Using NMR to follow the interaction of Au(THT)Cl with the functionalized siloxane, it was determined that the amine ligands displaced the THT ligand effectively. By comparison with other functionalized siloxane oligomers/compound, parameters such as density of ligating groups, oligomer steric barrier and reduction rates were found to be essential for the formation and stability of subnanometer Au particles. Without further treatment, the formed Au particles were active catalysts for the reduction of p-nitrobenzaldehyde by triethylsilane, forming an imine as the major coupling product. Deposition of the Au colloids onto silica, followed by thermal treatment to remove the organic groups resulted in subnanometer Au on silica, indicating this to be a promising method of fabricating subnanometer supported Au catalyst.

The ability of Au catalysts to effect the challenging task of utilizing molecular oxygen for the selective epoxidation of cyclooctene is fascinating. Although supported nanometre-size Au particles are poorly active, here we show that solubilized atomic Au clusters, present in ng ml−1 concentrations and stabilized by ligands derived from the oxidized hydrocarbon products, are active. They can be formed from various Au sources. They generate initiators and propagators to trigger the onset of the auto-oxidation reaction with an apparent turnover frequency of 440 s−1, and continue to generate additional initiators throughout the auto-oxidation cycle without direct participation in the cycle. Spectroscopic characterization suggests that 7–8 atom clusters are effective catalytically. Extension of work based on these understandings leads to the demonstration that these Au clusters are also effective in selective oxidation of cyclohexene, and that solubilized Pt clusters are also capable of generating initiators for cyclooctene epoxidation., Gold catalysts have previously been reported for the epoxidation of alkenes with molecular oxygen. Here the authors show that, rather than the gold nanoparticles, the active species for this reaction are actually small, soluble gold species stabilized by the oxidised organic products.

The importance of proximity of isolated TiOx cluster to Au surface for the formation of acetone in the selective oxidation of propane was investigated using a model system of Au particles decorated with mononuclear TiOx units dispersed in silica clusters. The results showed that no acetone was formed without TiOx, and its formation was more prominent on a sample containing a higher density of TiOx. Covering a Au/TiO2 catalyst with a layer of TiOx-containing silica changed the product selectivity from predominently propene to acetone. The data strongly supported the importance of isolated TiOx clusters near the Au surface in acetone formation, and suggested the relevance of Au-TiOx interface sites. Such interface sites might also be important in selective propene epoxidation that was coupled to CO oxidation in a H2O-methanol mixture. Using oxygen isotope labeling technique, it was found that the proximal source of oxygen in propene oxide was not from H2O but from O2. The observation was consistent with a methyl hydroperoxide intermediate, which could be formed by oxidation of a Ti methoxy at the Au-support interface.

The desire to attain high activity and selectivity achieved by systems in Nature has long been a source of inspiration for research in heterogeneous catalysis, and significant progress has been made. A summary is presented here of the progress in applying concepts in enzymes and cellular systems to develop artificial systems. The discussion is organized according to the length scale: dimensions of small molecules (~1 nm), protein (nm–μm), and cells (~μm). At the smallest dimension, the focus is on the active site, and effects observed include functional group cooperation, substrate partitioning, site isolation, transition state stabilization, and pK shifts. At the intermediate dimension of a protein, effects observed include size exclusion, steric constraint, and docking and induced fit. Interestingly, the oscillation phenomenon observed in artificial systems, which is due to collective behavior of atoms, is not observed in natural systems. At the largest, cellular scale, processes of interest include cascade reaction and tandem reactions, and metabolon is one natural system to emulate. There are interesting but nascent developments to emulate phenomena such as self-healing, stimuli-responsiveness, reaction coupling, and designed hierarchical distribution of pores and channels across all scales. Much could be gained if catalysts can be designed to incorporate these properties. .

Free-standing N-doped graphene papers (NGP), generated by pyrolysis of polydiallyldimethylammonium chloride, were successfully used as binder-free electrodes for the state-of-the-art Li/polysulfide-catholyte batteries. They exhibited high specific capacities of approximately 1000 mA h g(-1) (based on S) after 100 cycles and coulombic efficiencies great than 98%, significantly better than undoped graphene paper (GP). These NGP were characterized with XRD, X-ray photoelectron spectroscopy, thermogravimetric analysis, AFM, electron microscopy, and Raman and impedance spectroscopy before and after cycling. Spectroscopic evidence suggested stronger binding of sulfide to NGP relative to GP, and modelling results from DFT calculation, substantiated with experimental data, indicated that pyrrolic and pyridinic N atoms interacted more strongly with Li polysulfides than quaternary N atoms. Thus, more favorable partition of polysulfides between the electrode and the electrolyte and the corresponding effect on the morphology of the passivation layer were the causes of the beneficial effect of N doping.

A lithium sulfide-reduced graphene oxide nanocomposite (Li2S-rGO) was synthesized and evaluated as the cathode material and Li source for the assembly of Li-S batteries. The composite, with a unique 3-D pocket structure, was synthesized by a combination of facile solution chemistry and thermal treatment. The as-prepared Li2S-rGO nanocomposites were characterized by X-ray photoelectron spectroscopy, X-ray diffraction and scanning electron microscopy, which showed 20–40 nm Li2S particles homogeneously dispersed between reduced graphene oxide sheets. Li2S contents as high as ∼66% could be obtained. When used with an electrolyte containing LiNO3 and polysulfide, the Li2S-rGO nanocomposites exhibited a high initial capacity of 982 mAh g−1 Li2S. However, there was noticeable capacity fade in subsequent cycles, probably due to polysulfide dissolution and the shuttle mechanism, but a capacity of 315 mAh g−1 could still be obtained after 100 cycles, with 90–95% coulomb efficiency. The effect of polysulfide additive in the electrolyte on the activation of Li2S in the first delithiation step was discussed.

A discrete nanocage of core-shell design, in which carboxylic acid groups were tethered to the core and silanol to the shell interior, was found to react with Co2(CO)8 to form and stabilize a Co(I)-CO species. The singular CO stretching band of this new Co species at 1958 cm(-1) and its magnetic susceptibility were consistent with Co(I) compounds. When exposed to O2, it transformed from an EPR inactive to an EPR active species indicative of oxidation of Co(I) to Co(II) with the formation of H2O2. It could be oxidized also by organoazide or water. Its residence in the nanocage interior was confirmed by size selectivity in the oxidation process and the fact that the entrapped Co species could not be accessed by an electrode.

Organosilicon compounds, in the form of cubic metallasiloxanes, cage-like silsesquioxanes, macromolecular nanocages, and flexible structures such as dendrimers and linear metallsiloxanes, have found useful applications as catalysts, ligands for metal complexes, and catalyst supports. Illustrative examples of these are presented. The well-defined structures of these compounds make them particularly suitable as molecular analogues of zeolites or silica-supported catalysts. A unique feature of many of these compounds is the presence of flexible siloxane bonds, which accommodate large fluctuations in the framework geometry, reminiscent of the adaptability of enzymes to conformational changes, and distinguish siloxane containing materials from carbon based synthetic materials. New preparative pathways and the use of the versatile silyl ester as a protection group have greatly expanded synthetic possibilities, pointing to the possibility of assembling these structures to form multifunctional catalytic structures. Some nanocage structures, with functionalities organized in close proximity, exhibit nanoconfinement effects.

A thermally responsive membrane separator, suitable for use in non-aqueous electrolytes, was constructed by grafting a UCST polymer, poly(sulfobetaine), onto graphene oxide sheets. When heated from 20 to 80 °C, it decreased the specific storage capacity of the electrode for Li by >50% reversibly, compared to 30% increase without polymer modification.

The effect a 45 atom-thick overlayer of aluminum oxide, deposited by atomic layer deposition, was investigated on a 2.5 wt.% Pd/Al 2 O 3 catalyst in which the Pd nanoparticles were encapsulated by the support consequent to the preparation method. The overlayer suppressed the activity for oxidative dehydrogenation of ethane, but it also effectively prevented metal sintering and suppressed coking for reactions at high temperatures. On the catalyst with the alumina overlayer, a steady activity was observed even at 600 °C and above when the gaseous oxygen was completely consumed, while attaining 70% selectivity for ethene at 38% conversion, versus 10% selectivity at comparable conversions without the overlayer. The overlayer preferentially deposited on edge Pd atoms, as indicated by preferentially suppression of the CO chemisorption peak at 2056 cm −1 , which are responsible for coking. The high ethene selectivity at 675 °C could be due to coupled homogeneous and heterogeneous reactions at the high temperature, together with phase change of PdO to Pd.

Mild calcination in ozone of a (POSS)-Sn-(POSS) complex grafted on silica generated a heterogenized catalyst that mostly retained the tetrahedral coordination of its homogeneous precursor, as evidenced by spectroscopic characterizations using EXAFS, NMR, UV–vis, and DRIFT. The Sn centers are accessible and uniform and can be quantified by stoichiometric pyridine poisoning. This Sn-catalyst is active in hydride transfer reactions as a typical solid Lewis acid. However, the Sn centers can also create Bronsted acidity with alcohol by binding the alcohol strongly as alkoxide and transferring the hydroxyl H to the neighboring Sn–O–Si bond. The resulting acidic silanol is active in epoxide ring opening and acetalization reactions.

Surface species formed in CH4 activation over Co–ZSM-5 were monitored by in situ DRIFT spectroscopy. IR absorption bands assigned to adsorbed methoxide, formate and polyoxymethylene were detected. The similarities in the IR bands and their evolution during He purge after reactions conducted under anaerobic and aerobic conditions suggested that Cannizzaro disproportionation of formaldehyde is a significant reaction pathway. This was verified when water was found to react with a surface species to form adsorbed formate. Continued formation of surface formate was observed during purging in He which indicated substantial surface storage of formaldehyde as polyoxymethylene.

Two types of dendrimers with AB2 branching, one with acyloxysilanes at the branching position (V type) and the other at the non-branching position (Y type), were synthesized using hydrosilylation with chlorosilanes followed by heterofunctional condensation with olefin-functional carboxylic acids, and examined as readily degradable template materials. The V type dendrimer was much more susceptible to ligand redistribution with chlorosilanes during preparation, whereas the Y type was less. The acyloxysilane linkages in these dendrimers could be cleaved readily by alcoholysis or hydrolysis on demand, making for suitable templates.

A tetrahedral stannasilsesquioxane complex was synthesized as a racemic mixture using Sn(O(i)Pr)4 and silsesquioxanediol, and its structure was confirmed with X-ray crystallography, NMR, and EXAFS. The complex was a Lewis acid, and both anti and syn-binding with Lewis bases were possible with the formation of octahedral Sn complexes. It was also a Lewis acid catalyst active for epoxide ring opening and hydride transfer.

A combination of two synchrotron X-ray techniques, X-ray absorption spectroscopy (XAS), and pair distribution function analysis (PDF) with complementary Fourier transform infrared (FTIR) spectroscopy measurement, was used to characterize the composition distributions of PdAu and PtCu bimetallic particles after treatment in H2 or CO and in the presence of these gases. This is the first reported application of PDF to the study of supported bimetallic nanoparticles. We found that XAS was informative in determining the component distribution of an initial sample, but PDF was better suited to following changes in the distribution upon changing the gas environment. Thus, the surface of a PtCu bimetallic particle of about 2.5 nm after treatment in H2 was found to be enriched in Cu, while the core was bimetallic. There was no evidence of a component-segregated core−shell structure. Treatment in CO caused enrichment of Pt to the surface layer, with a concomitant migration of Cu to the core. The average particle si...

A combination of two catalysts, Au/TiO2 and TS-1 were used to catalyze the demanding reaction of butene epoxidation in an aqueous solution using molecular oxygen under very mild reaction conditions. Peroxy initiator was not necessary but carbon monoxide as a sacrificial reductant was needed. Carbon monoxide conversions increase with time on stream suggesting the generation of a highly active aqueous phase CO oxidation catalyst.

Advances in understanding enzyme catalysis have made possible development of synthetic schemes and strategies to incorporate the essential functions of enzymes into artificial structures. Two of these functions, environmental effect inherent to the active site cavity defined by the protein conformation and cooperative effect of functional groups in the cavity, have been successfully introduced into artificial structures and examined. Illustrative examples of these studies are described, as well as remaining challenges and illustrative application potentials.

Two approaches to synthesize silicon-based catalytic structures that aim at capturing the properties and functionalities of natural enzymes are described in this brief review: unit-by-unit synthesis of macromolecular units and templating/imprinting synthesis of nano-cages. The unit-by-unit approach mimics the peptide synthesis method, offers atomic control of the structure, but is inefficient in synthesizing large structures such as nanocages. The templating/imprinting method is more suitable for nanocages at the sacrifice of atomic control, and the nanocages obtained are shown to possess properties exhibited by enzyme cavities.

The reduction of NO, at 185 °C on Pd supported on Ti-pillared clay was studied using H 2 and CO generated by reforming of ethylene glycol (EG) over a Na-Pt/γ-Al 2 O 3 catalyst. It was found that for a stream containing 490 ppm NO, 5.8% Ο 2 , and 2.9% H 2 O, at a space velocity of ∼24,000 h -1 , a stable NO x conversion of ∼55% was obtained when a stream of 1.36% EG was reformed under a condition that the EG conversion was complete and sufficient H 2 and CO was produced. However, if the EG conversion was incomplete, the unreacted EG deactivated the deNO x catalyst, possibly by coking, that could not be regenerated by O 2 treatment at reaction temperature. H 2 O suppressed the deNO x activity, but the effect was reversible and the activity could be recovered after removal of H 2 O. The deNO x activity was found to be higher on catalysts containing more highly dispersed Pd.

Whereas cooperative effect in catalysis, in which multiple chemical interactions participate cooperatively to achieve significant enhancement in catalytic activity and/or selectivity, is common in enzymatic reactions, it has been sparingly employed in heterogeneous catalytic systems. Here, some recent literature examples of abiotic catalysis, with emphasis on heterogeneous systems, that employ cooperation between acid and base and two metal centers are briefly described to demonstrate the principles involved. Since effective cooperation places strict demand on the positions of the different functional groups, new synthetic methods and strategies are needed to design and construct structures useful for cooperative catalysis. Recent progress in our laboratory in synthesizing new nanocage structures that possess molecular-size cavities, atomic layer thick, porous shells with internal functional groups is described. These recent developments suggest possibilities of new catalytic transformations that have not been attempted before. This is illustrated with two speculative examples utilizing cooperative catalysis: oxidative hydrolytic desulfurization and terminal carbon activation of hydrocarbon molecules.

The effect of halide poisoning of Au/TiO{sub 2} catalysts in low temperature CO oxidation was investigated using bromide as the poison and a combination of X-ray absorption spectroscopy (XANES and EXAFS), quantitative CO adsorption, and catalytic measurements. It was found that halide prevented full reduction of cationic Au by displacing oxyhydroxy ligands and remaining bound to Au during low temperature reduction, causing a reduction in catalytic activity. On reduced Au samples, bromide (likely as NaBr molecule) was preferentially adsorbed on Au and not on TiO{sub 2}, and suppressed both the adsorption of CO and the catalytic activity. At low Br contents, each adsorbed Br suppressed adsorption of three CO, suggesting that Br was adsorbed on three-fold sites but the effect decreased with increasing Br content possibly due to crowding of adsorbed Br. When 5--10% of the Au was bound to Br, the catalytic activity was completely blocked, although {approx}35% of the original CO adsorption capacity remained. The data suggest that not all CO adsorption sites are catalytic active sites, and are consistent with the perimeter Au atoms at/near the particle-support interface (perimeter) being active sites.

The epoxidation of 1-hexene with titanium silicalite-1 (TS-1) catalyst was investigated to gain insight into the effect of the solvent on the observed reactivity. Three different solvents were examined: methanol, acetonitrile, and acetone. Kinetic data were obtained from batch reaction experiments, with an emphasis placed on gathering more accurate initial rates than those reported in the literature. The dependencies of the rates on the concentrations of 1-hexene, water, and hydrogen peroxide were determined. The adsorption behavior of 1-hexene in TS-1 in the three different solvents was determined independently by batch sorption experiments. Results showed that the solvent has a significant effect on the adsorption of 1-hexene, and hence on the reaction kinetics. Kinetic modeling incorporating experimental and simulated quaternary adsorption isotherms to describe quasi-equilibrated steps revealed that the differences in the observed reaction kinetics may be attributed mostly, but not entirely, to differences of the partitioning of 1-hexene between the bulk and intraporous phases among the three different solvents.

Ethylene glycol (EG) reforming was investigated as a method to generate H2 and CO reductants for low-temperature lean NOx reduction. Stable production of H2 was obtained at 230 °C over a Pt/Al2O3 catalyst using a feed consisting of 2−5% O2 and >2.2% EG. The presence of H2O in the feed enhanced H2 production, as did Na modification of the catalyst. Water gas shift was determined not to contribute significantly to H2 production during EG reforming.

An efficient synthetic strategy for immolative carbamate dendrons and dendrimers is described that requires no protection/deprotection in the convergent growth step. 1,3-Diamino-2-propanol was used as AB 2 building block and 4-nitrophenyl chloroformate as carbamate forming reagent. The method was demonstrated with a G3-dendron. A combination of convergent and divergent growth method was used to couple G2-dendrons to a G2-core or G3-dendrons to a tetrahedral G1-core with amine functional groups to form a spherical carbamate dendrimer (G4) possessing an olefinic periphery.

Nanostructured membrane structures have been fabricated by a combination of anodic aluminum oxidation (AAO) and atomic layer deposition (ALD) for use as platforms for the synthesis of highly uniform heterogeneous catalysts. The ALD method makes it possible to control pore diameters on the Angstrom scale even when the overall pore diameter is 10’s to 100’s of nanometers. AAO membranes imbedded in an aluminum sealing ring have been tested for flow properties and found to follow Knudsen diffusion behavior. Vanadia-coated membranes have been tested for the catalytic oxidative dehydrogenation of cyclohexane and show improved selectivity at the same conversion compared to conventional powdered alumina supported vanadia catalysts.

The adsorption of CO and its reaction with oxygen were investigated using a combination of in situ Fourier transform infrared spectroscopy, step response measurements in a microreactor, (18)O isotopic labeling, and X-ray absorption near edge structure spectroscopy. An as-prepared sample in which Au is present as a surface oxyhydroxy complex does not adsorb CO. On an activated sample in which only metallic Au is detected, 0.18 +/- 0.03 mol CO/(mol Au) are adsorbed on Au at -60 degrees C, which shows an IR band at 2090 cm(-1). When oxygen is present in the gas phase, this species reacts with a turnover rate of 1.4 +/- 0.2 mol CO(mol Au min)(-1), which is close to the steady-state turnover rate. In contrast, there is a very small quantity of adsorbed oxygen on Au. A small IR peak at 1242 cm(-1) appears when an activated sample is exposed to CO. It reacts rapidly with oxygen and is shifted to 1236 cm(-1) if (18)O is used. It is assigned to the possible intermediate hydroxycarbonyl.

The catalytic performance of Au/Al 2 O 3 catalyst is highly sensitive to preparation procedure. EXAFS and TEM characterization of key steps in the preparation in conjunction with activity measurements result in deeper insights into precautions needed and the complex manner residual chloride impacts catalytic activity. Chloride affects the morphological (Au particle size), chemical (reducibility) as well as the catalytic (poisoning) properties of Au. Alternate preparation procedures to the conventional calcination of a catalyst prepared with deposition–precipitation at neutral pH were explored to increase Au loadings. It was found that low temperature H 2 reduction of a catalyst prepared at low pH but washed with NaOH is an effective preparation method.

Atomic layer deposition (ALD) on anodic aluminium oxide (AAO) is shown to be a facile, flexible route to the synthesis of catalytic membranes with precise control of pore wall composition and diameters. The oxidative dehydrogenation of cyclohexane was shown to depend strongly on pore diameter and to be more specific than similarly active alumina powder catalysts.

Anodic aluminum oxide (AAO) membranes were characterized by UV Raman and FT-IR spectroscopies before and after coating the entire surface (including the interior pore walls) of the AAO membranes by atomic layer deposition (ALD). UV Raman reveals the presence of aluminum oxalate in bulk AAO, both before and after ALD coating with Al2O3, because of acid anion incorporation during the anodization process used to produce AAO membranes. The aluminum oxalate in AAO exhibits remarkable thermal stability, not totally decomposing in air until exposed to a temperature900 degrees C. ALD was used to cover the surface of AAO with either Al2O3 or TiO2. Uncoated AAO have FT-IR spectra with two separate types of OH stretches that can be assigned to isolated OH groups and hydrogen-bonded surface OH groups, respectively. In contrast, AAO surfaces coated by ALD with Al2O3 display a single, broad band of hydrogen-bonded OH groups. AAO substrates coated with TiO2 show a more complicated behavior. UV Raman results show that very thin TiO2 coatings (1 nm) are not stable upon annealing to 500 degrees C. In contrast, thicker coatings can totally cover the contaminated alumina surface and are stable at temperatures in excess of 500 degrees C.

CO impedes the low temperature (